Methods which have been devised for determining blood flow characteristics include indicator dilution methods, magnetic flow meters, ultrasonic blood flow meters, impedance cardiography blood flow determination by radiographic methods and by a method which is known as the Fick Method.
These methods have proved to be inadequate to meet the needs of surgeons and others in medical practice at the present time.
My U.S. Pat. No. 3,996,925 describes a system for determining blood flow using electrical impedance across a section of a living body, and some of the characteristics of blood flow may be determined by this system with a fair degree of accuracy, but there is a long-standing need for a system which is more accurate and which is effective for determining many other characteristics of flood flow and which is sensitive to the variation of individual persons or sections of the body under test. For example, in the determination of rate of blood flow, it has been necessary to utilize a fixed or an average value as the modulus of elasticity (E) for the walls of blood vessels. It would, indeed, be desirable to known and to use a value for this modulus which is determined at the time as a result of sensing indications of the particular individual under test. Also, it would be very desirable to determine other characteristics such as cross-sectional area of the blood vessels and the variations of this area over a selected time period or during the cycle of blood flow, or at any particular times during the cycle.
Accordingly, I have set about to discover methods and means for accurately determining and displaying, or otherwise demonstrating, information as it is being produced about many blood flow characteristics, some of which have never before been demonstrted, at any instant of time, and to demonstrate the variation of such characteristics during a cycle, during any particular part of a cycle, or during any selected time period. Another of my objectives was to utilize additional indications obtained from the body under test and to eliminate the use of average or general constants as much as possible in making the determinations.